Tropical cyclone Hermine slowed its movement in the Atlantic on Sunday night and was preparing to park for a while off the Northeast coast, promising hammer-like waves, floods and beach erosion through Labor Day and beyond.

At 11:30 p.m. ET, Hermine was about 325 miles southeast of the eastern tip of Long Island, N.Y., all of which was under threatening storm-surge advisories Sunday night.

Hermine was still packing maximum sustained winds of 70 mph, just short of hurricane strength — and it's expected to remain near hurricane strength through Monday evening.

The National Weather Service said large waves will pound the East Coast from the mid-Atlantic states to southern New England through Monday night. Life-threatening rip currents are expected at least into the middle of the week, the weather service said.

Tropical storm warnings were concentrated along the coast Sunday from New York, New Jersey and Connecticut coasts, including the counties north and east of New York City. Suffolk County, N.Y., Executive Steven Bellone issued a voluntary evacuation order for the South Shore of Long Island and for Fire Island, the large barrier island that runs parallel to it.

Hermine has been moving east since it battered Florida and the Carolinas on its way up the coast beginning Friday. But updated National Weather Service projections indicated that its eastward motion is ending and that it's likely to slowly veer northwestward through Tuesday — that is, back toward the Northeast coast.

"I certainly would not suggest going in the water the next couple of days," said Ari Sarsalari, a meteorologist for The Weather Channel. "The storm surge is not as bad as expected, but the rip currents are going to be really bad."

"It's disappointing, but you understand you've got to weigh safety versus the enjoyment of the weekend," Greg Mattesen of Portland, Maine, who was visiting Hammonasset Beach State Park, told NBC Connecticut. "I can kind of understand it, but it's disappointing."

In Milford, Conn., "we have all of our furniture up against the house and just hope and pray nothing major happens," Tina Capozzi told NBC Connecticut.

The Red Cross put out a call for more volunteers in the Northeast, noting that many of its resources are still deployed in Florida and the Carolinas.

Farther south, vacationers who fled the beaches Friday and Saturday kept business owners busy figuring out just how much revenue they'd lost.

"We live by the weather and we die by the weather," said Louis Gouvas, who's owned Louie's Pizza in Rehoboth Beach, Del., for almost 60 years.

A red flag warns visitors to stay out of the water Sunday at Rehoboth Beach, Del., where business owners say they could lose as much as 75 percent of their Labor Day weekend revenue.NBC News Channel

Gouvas told NBC Washington on Sunday that he estimated his Labor Day weekend business will turn out to be 60 percent below normal. Other businesses along the beach's crowded boardwalk could be down as much as 75 percent, he said.

In the artsy seaside village of Cedar Key, Fla., "it's going to be a slow recovery," Police Chief Virgil Sandlin told NBC station WTLV of Jacksonville.

About a third of the island is flooded, said Sandlin, who estimated economic losses at "10-plus million dollars, easily."

In Pasco County, just north of Tampa, meanwhile, run-off from flooded northern parts of the state washed over roads and through houses, the sheriff's office said.

Lynne Garrett speaks to loved ones on the phone as she surveys damage outside her home Friday in Tampa, Fla.Brian Blanco / Getty Images

Lenny Panzitta joined friends and neighbors who spent Sunday sawing up downed trees that were blocking the roads on Whitemarsh Island, off the Savannah, Ga., coast.

Then "the electricity went off, and I said I hope another tree didn't come down where they were clearing, and it did," Panzitta told NBC station WSAV of Savannah.

"It knocked the transformer down," he said. "Nobody was hit, but now we have wires hanging over the road so you can't get through."

North Carolina Gov. Pat McCrory and other state officials spent the day touring farm damage in the eastern part of his state, where thousands of acres of crops remained under water.

Farms adjacent to federal fish and wildlife refuges flood frequently, even though those lands aren't equipped to handle heavy rain. So the runoff runs onto their land, drowning their crops, several farmers said.

"This farm can't drain, so not only am I holding my 5 inches, I'm holding a good portion of that refuge water on my land," Tyrell County soybean farmer Jett Ferebee told NBC station WRAL of Raleigh.

McCrory told the farmers he's working with the federal government to protect farmers from similar problems in future storms.

Alex Johnson

Alex Johnson is a senior writer for NBC News covering general news, with an emphasis on explanatory journalism, data analysis, technology and religion. He is based in Los Angeles.